1. Field of the Invention
This invention relates, in general, to a construction of sewing machines and, in particular, to a new and useful guiding device for sewing machines having means for feeding cloth workpieces into association with a moving needle to effect edged parallel seams and with two plates forming a passageway and a pressure point for a cloth layer arranged laterally of the stitch forming area and wherein the top plate can be moved vertically relative to the bottom plate and which includes a ruler arranged laterally at an acute angle to a line extending through the feed direction of the workpiece through the needle axis.
2. Description of the Prior Art
A known sewing machine workpiece guiding device has three plates for the separate contour control of two workpiece layers, which come in contact with each other under initial stress at a point laterally in front of the stitch forming area to form a pressure point for each workpiece layer. In this way a braking action is exerted on each individual workpiece layer during the feed in the range of the pressure points, so that each workpiece layer performs a rotary movement independent of the other workpiece layer, and thus bears on a ruler which extends in an acute angle to a line extending in feed direction through the needle axis. Between the plates are arranged spacers at the ends opposite the pressure points in the proximity of the ruler. The spacers are replaceable to adapt the vertical plate distances to different cloth thicknesses. But this method is cumbersome and time-consuming if the cloth thicknesses change frequently. Besides it requires the keeping of a stock of a great number of spacers of different thickness.
In another known guiding device the central and top plate are arranged on the bottom plate by means of a hinge with a horizontal axis of rotation. The ruler for the edge of the workpiece layers to be aligned is formed by several stop pins secured in the bottom plate and protruding through corresponding openings in the other two plates. The pressure of the plates in the range of the pressure points is produced by the weight of the plates. In order to be able to adapt the pressure to different cloth thicknesses, each plate is adjustable by means of its adjusting mechanism in its vertical position relative to the respective bottom plate. The distance between the ruler and the hinge is selected relatively great, so that the central and top plate are not overly inclined when sewing workpieces with a great cloth thickness, but still the disadvantage of this device is substantially the same as in the abovementioned device. If the plates are arranged at a small distance one above the other for the proper guidance of thin workpiece layers, a friction which hinders the alignment, is exerted on the workpiece layers in the case of thick layers, due to the resulting inclined position of the plate by the parts of the plates close to the stop pins. It was also found that a satisfactory alignment can only be achieved in workpieces with a great cloth thickness if a much greater pressure is exerted at the pressure points than in workpieces with medium or smaller cloth thickness. This requirement can only be met very unsatisfactorily in a device where the pressure is produced by the weight of the plates.